Polymers containing
sulfur centers with high oxidation states in
the main chain, polysulfoxide and polysulfone, display desirable properties
such as thermomechanical and chemical stability. To circumvent their
challenging direct synthesis, methods based on the oxidation of a
parent polysulfide have been developed but are plagued by uncontrolled
reactions, leading either to ill-defined mixtures of polysulfoxides
and polysulfones or to polysulfones with reduced degrees of polymerization
due to overoxidation of the polymer. We developed an alternative method
to produce well-defined polysulfoxide and polysulfone in a waterborne
colloidal emulsion using different oxidants to control the oxidation
state of sulfur in the final materials. The direct oxidation of water-based
polysulfide latexes avoided the use of volatile organic solvents and
allowed for the control of the oxidation state of the sulfur atoms.
Oxidation of parent polysulfides by
tert
-butyl hydroperoxide
led to the production of pure polysulfoxides, even after 70 days of
reaction time. Additionally, hydrogen peroxide produced both species
through the course of the reaction but yielded fully converted polysulfones
after 24 h. By employing mild oxidants, our approach controlled the
oxidation state of the sulfur atoms in the final sulfur-containing
polymer and prevented any overoxidation, thus ensuring the integrity
of the polymer chains and colloidal stability of the system. We also
verified the selectivity, versatility, and robustness of the method
by applying it to polysulfides of different chemical compositions
and structures. The universality demonstrated by this method makes
it a powerful yet simple platform for the design of sulfur-containing
polymers and nanoparticles.
Thiol-ene polymerization is a powerful synthetic platform for the preparation of a variety of polymer materials but is often plagued by the formation of low molecular weight polymers. This is...
This study is about multiple responsiveness in biomedical materials. This typically implies "orthogonality" (i.e., one response does not affect the other) or synergy (i.e., one increases efficacy or selectivity of the other), but an antagonist effect between responses may also occur. Here, we describe a family of very well-defined amphiphilic and micelle-forming block copolymers, which show both oxidative and temperature responses. They are produced via successive anionic ring-opening polymerization of episulfides and RAFT polymerization of dialkylacrylamides and differ only in the ratio between inert (N,N-dimethylacrylamide, DMA) and temperature-sensitive (N,Ndiethylacrylamide, DEA) units. By scavenging Reactive Oxygen Species (ROS), these polymers are anti-inflammatory; through temperature responsiveness, they can macroscopically aggregate, which may allow them to form depots upon injection. The localization of the anti-inflammatory action is an example of synergy. An extensive evaluation of toxicity and anti-inflammatory effects on in vitro models, including BV2 microglia, C8D30 astrocytes and primary neurons, shows a link between capacity of aggregation and detrimental effects on viability which, albeit mild, can hinder the anti-inflammatory potential (antagonist action). Although limited in breadth (e.g., only in vitro models and only DEA as a temperature-responsive unit), this study suggests that single-responsive controls should be used to allow for a precise assessment of the (synergic or antagonist) potential of doubleresponsive systems.
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